The present invention relates to a method of controlling the boost pressure of a blower, known as a supercharger or a turbocharger, associated with an internal combustion engine.
Blowers such as superchargers or turbochargers are generally driven by the power output from the output shaft of or the exhaust gases emitted from engines. As the rotational speed of the engine goes higher, the driving force for the blower is also increased and the boost pressure thereof becomes higher. Since an excessive boost pressure would cause troubles such as knocking, it would be preferable to control the boost pressure at an optimum level under all conditions. In the supercharger operated by the engine power output, the boost pressure can be controlled by selectively applying and cutting off the driving force to and from the supercharger or opening and closing a bypass valve. In the turbocharger operated by the engine exhaust gases, the boost pressure can be controlled by adjusting movable vanes to restrict the exhaust gas supplied to the turbine wheel or selectively opening and closing a wastegate.
All types of blowers are subject to a certain type delay in the response of the boost pressure to the engine rotational speed or the throttle valve. Therefore, under normal feedback control, the boost pressure that is controlled tends to overshoot excessively or undergo hunting if control characteristics are not appropriate. If the feedback control were to be stabilized so as to be less responsive to the parameters, the response of the control system would be greatly impaired. It has been found that the intake air temperature and the atmospheric pressure are important as control parameters.
Where open-loop control such as map control is relied upon, no control stability problem occurs. Since, however, many parameters are involved and many map addresses or locations are required, a control unit used should have a large memory capacity and may be retarded in its response speed.